Field of the Invention
The present invention relates to a solid-state light-receiving device for ultraviolet light.
Description of the Background Art
Recently, fields that use a solid-state light-receiving device for ultraviolet light have increased in variety and are showing a trend toward further increase in the future.
Within these fields, ultraviolet (UV) protection for protecting the skin against the ultraviolet rays of sunlight has been a significant issue for humankind from the viewpoint of not only beauty, but also the prevention of skin cancer. As a result, the market for a solid-state light-receiving device for ultraviolet light for UV protection is trending toward further increase in the future.
Furthermore, the threat of ultraviolet light (UV rays; ultraviolet rays) in association with the formation and expansion of ozone holes as well as the fear of skin cancer caused by UV ray irradiation, in particular, pertain to all humans, not just those in the southern hemisphere where there is significant ozone hole expansion, making countermeasures therefor a great concern.
On the other hand, a light suntan still serves as a foundation for health and attractiveness, and often the young actively bathe in the sun. Furthermore, from the viewpoint of health maintenance, sun exposure is required to obtain vitamin D. From these viewpoints, bathing in the sun while avoiding ultraviolet light harmful to the human body (UV-A: 315 to 380 nm wavelength, UV-B: 280 to 315 nm wavelength, UV-C: 280 to 200 nm or less wavelength) is strongly encouraged.
Such UV protection for protecting the skin and the like from harmful ultraviolet rays include the promotion of sunburn protection (UV protection) by using goods such as hats, elbow-length gloves, and umbrellas, wearing long-sleeve shirts, and applying sunburn prevention cosmetics as well as pharmaceuticals to exposed skin, on a daily basis. However, the amount of ultraviolet rays in sunlight is significant not only under a blazing sun in midsummer, but also under cloudy conditions, and UV protection tends to be neglected now and then on cloudy days. Furthermore, when a person is out and the weather suddenly changes to that having a significant amount of ultraviolet rays, more often than not UV protection is not adequately applied. Hence, recently, to measure ultraviolet rays and ensure the establishment of appropriate UV protection, mobile ultraviolet light sensors (solid-state light-receiving devices for ultraviolet light) have started to be proposed and commercialized.
In addition of the fields of sunlight UV protection described above, the large market of solid-state light-receiving devices for ultraviolet light includes the following fields.
That is, the large market includes analytical device fields such as measuring devices, atomic absorption analysis, high-performance liquid chromatography (HPLC), and exhaust gas analysis; chemical analysis fields and industrial application fields such as sterilization, food processing, solvent-free organic and inorganic material surface cleaning and treatment, glass and plastic substrate material bonding, and static electricity removal; medical application fields such as DNA cleavage and eye care; and semiconductor lithography equipment fields. These fields are expected to grow in importance and expand in market size, and international competition among countries is expected to intensify in the future.
In these fields, ultraviolet rays of a wavelength region of 400 nm or less are used. While the wavelength region differs somewhat according to the method of classification, the ultraviolet rays of each classified wavelength region are given the names below.
Near ultraviolet rays (wavelength: 380 to 200 nm)
UV-A (wavelength: 380 to 315 nm)
UV-B (wavelength: 315 to 280 nm)
UV-C (wavelength: 280 to 200 nm)
Far ultraviolet rays (far UV, FUV) or vacuum ultraviolet rays (vacuum UV, VUV) (hereinafter together referred to as far ultraviolet rays) (wavelength: 200 to 10 nm)
Extreme ultraviolet rays (extreme UV, EUV, or XUV) (wavelength: 10 to 1 nm)
However, in photolithography and laser technology, deep ultraviolet rays (deep UV, DUV) differs from FUV described above, and refers to ultraviolet rays having a wavelength of 300 nm or less.
Examples of representative fields of ultraviolet application by wavelength region, or fields in which market expansion is expected in the future, include the following:
(1) Extreme ultraviolet rays (EUV) having a wavelength of 13.5 nm
Semiconductor lithography, liquid immersion lithography
Beam line: Resist and mask evaluation
Extreme-ultraviolet imaging spectrometers (EIS) that carry out spectroscopic observations and solar atmospheric diagnoses in the extreme ultraviolet region
Microelectronics, nanoscale processing
Living cell holography
High-temperature, high-density plasma diagnostics
X-ray microscopes
(2) Deep ultraviolet light-emitting diodes (LEDs) (wavelength: 200 to 350 nm)
This range is increasing in importance across a wide variety of fields, from information and electronic devices to safety & health, environmental, and medical applications.
High-density optical information recording
Bacteria and virus sterilization, drinking water and air purification
Biosensing
Biomaterial analysis
Optical lithography
In-hospital infection prevention, photo-surgery treatment
Ultraviolet irradiation devices (excimer irradiation devices, LED irradiation devices)
Oxide film removal, surface modification, dry cleaning, UV curing, adhesion, drying
In these fields, use of vacuum ultraviolet light sources, Xe excimer light sources, and deuterium lamps (D2Ls) having a light emission intensity in a far ultraviolet bandwidth of about a 200-nm light wavelength and a vacuum ultraviolet bandwidth of about a 200-nm or less wavelength has increased, and this trend is expected to continue in the future.
As light level monitor means for a light source used in these applications, a solid-state light-receiving device for ultraviolet light is required.
However, in a solid-state light-receiving device for ultraviolet light for a light level monitor or a mobile ultraviolet light sensor used for UV protection, an amount of light in the ultraviolet bandwidth often needs to be accurately measured with ambient light existing in the background.
For example, sunlight includes ultraviolet light as well as visible light and infrared light. Thus, when an amount of irradiation of ultraviolet light is measured, the amount of irradiation of ultraviolet light cannot be accurately measured unless the effects of light rays other than ultraviolet light on measured values are avoided.
A solid-state light-receiving device for ultraviolet light for a light level monitor or a mobile ultraviolet light sensor used for UV protection has spectral response characteristics of that wide range, and a solid-state light-receiving device for ultraviolet light that uses bulk silicon (Si) as a semiconductor substrate (hereinafter also expressed as “bulk Si-type solid-state light-receiving device for ultraviolet light”) is representative of such a device.
In the case of the bulk Si-type solid-state light-receiving device for ultraviolet light, the silicon (Si) layer is sensitive to ultraviolet light as well as visible light and infrared light, and therefore requires, for example, a visible light and infrared light cut optical filter, which increases costs.
One example of a solution to this problem is the use of a thin film silicon on insulator (SOI) substrate (Non-Patent Documents 1 and 2).
The UV sensors set forth in Non-Patent Documents 1 and 2 utilize the relative ease of the transmission of visible and infrared light with a thin SOI layer, making the UV sensors have selectively high sensitivity to light mainly having a wavelength of 400 nm or less.
In addition, for example, there is a light-detecting device for ultraviolet light detection (solid-state light-receiving device for ultraviolet light) set forth in Patent Document 1.
The light-detecting device set forth in Patent Document 1 is made of MgXZn1-XO (0≤X<1), comprises a first light-detecting portion that includes a light-absorbing semiconductor layer that absorbs light of a wavelength range λ further on a light-receiving surface side than a photoelectric conversion region, and a second light-detecting portion that includes a transmitting film without a light absorption region further on the light-receiving surface side than the photoelectric conversion region. This light-detecting device measures the amount of light in the wavelength range λ by calculating signals of the first light-detecting portion and signals of the second light-detecting portion.